JP2872543B2 - Thermally bonded nonwoven fabric and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-bonded nonwoven fabric made of a polyolefin-based fine fiber having a core-sheath type composite short fiber and a method for producing the same. This non-woven fabric is strong, very bulky and extremely excellent in water retention, and has no slimy feeling unique to polyethylene, very good texture,
Has a good texture. Therefore, it is particularly suitable for use in medical hygiene materials such as disposable diapers and sanitary napkins. In addition, since it has chemical resistance and excellent water retention, it is particularly suitable as a battery separator.
In addition, it can be suitably used for a wide range of applications, such as agricultural and horticultural materials, packaging materials and filters as living-related materials.

[0002]

2. Description of the Related Art Conventionally, heat-bonded short-fiber nonwoven fabrics have been used for various purposes such as clothing, industrial materials, civil engineering and construction materials, agricultural and horticultural materials, living-related materials, and medical hygiene materials. I have.

[0003] In nonwoven fabrics for medical hygiene materials such as disposable diapers and coated papers for sanitary absorbents, the demand of which has been rapidly increasing in recent years, a soft and soft texture is required. In addition, demand for nonwoven fabrics for electrical and electronic equipment is expanding, and in this field, nonwoven fabrics are also required to have good chemical resistance and excellent water retention. In order to satisfy these required qualities as much as possible, a method of producing a non-woven fabric by a thermal through-type or emboss-type thermal bonding method is mainly used.

[0004] These nonwoven fabrics are obtained by using composite fibers containing a fiber-forming polymer having a different melting point as a composite component.
JP-B-42-21318, JP-B-44-2254
No. 7, Japanese Patent Publication No. 52-12830, Japanese Patent Publication No. 61
It is known in, for example, Japanese Patent Publication No.

[0005]

The low-melting-point component of conventionally used composite heat-bonding fibers for nonwoven fabrics usually includes
Polyester and polyethylene are used. Nonwoven fabrics composed of composite heat-bonded fibers containing polyethylene as a low melting point have a slimy feeling unique to polyethylene, which makes some people feel uncomfortable, and the fineness of fineness due to the poor spinnability of polyethylene itself. However, there was a problem that the fibers of the formula (1) could not be obtained.

Further, the present inventors have disclosed in Japanese Patent Laid-Open No.
No. 93958 proposes a spun-lace nonwoven fabric made of ultrafine polyolefin-based core-sheath composite short fibers.
The nonwoven fabric is processed by a spunlace method so that its softness is not impaired.However, since it is a perforated nonwoven fabric, there is a problem that its use is limited such as being unsuitable for a battery separator or other uses. there were.

[0007] An object of the present invention is to solve the above-mentioned problems and to provide a nonwoven fabric having a very good texture and a good texture.
Moreover, it is an object of the present invention to provide a polyolefin-based heat-bonded nonwoven fabric having practical performance, excellent chemical resistance, and excellent water retention.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have reached the present invention. That is, the present invention provides (1) a sheath portion formed of a blend structure of an ethylene-based polymer and a propylene-based polymer, and a core portion of the propylene-based polymer; A heat-bonded nonwoven fabric made of core-sheath composite short fibers of 2 to 1 denier and bonded at contact points between the fibers; and (2) an ethylene-based polymer in which propylene is copolymerized. And a core-sheath type composite short fiber having a single yarn fineness of 0.2 to 1 denier. (3) a sheath portion formed of a blend structure of an ethylene-based polymer and a propylene-based polymer, and a core portion of the propylene-based polymer. And a core-sheath type composite short fiber having a single yarn fineness of 0.2 to 1 denier. A method for producing a heat-bonded nonwoven fabric, wherein the card web is heat-treated with hot air so as to satisfy the following equation, and bonded at a contact point between fibers; and a heat treatment temperature T (° C.) Tm1 ≦ T <Tm2- 10 Heat treatment time t (min) 0.1 ≦ L / v, L / v = t Tm1: Melting point (° C.) of ethylene polymer in sheath portion Tm2: Melting point (° C.) of propylene polymer in core portion L: Heat treatment zone length (m) v: Heat treatment rate (m / min) (4) Having a sheath formed of an ethylene polymer in which propylene is copolymerized and a core of the propylene polymer. Then, a card web composed of a core-sheath composite short fiber having a single yarn fineness of 0.2 to 1 denier is heat-treated with hot air so as to satisfy the following formula, and bonded at a contact point between the fibers. A method for producing a heat-bonded nonwoven fabric, characterized in that the heat treatment temperature T (° C.) Tm1 ≦ <Tm2-10 Heat treatment time t (min) 0.1 ≦ L / v, L / v = t Tm1: Melting point of ethylene polymer in sheath (° C.) Tm2: Melting point of propylene polymer in core (° C.) ) L: heat treatment zone length (m) v: heat treatment speed (m / min)

Next, the present invention will be described in detail. First, the core-sheath type composite short fiber constituting the nonwoven fabric of the present invention will be described. The sheath portion of the core-sheath type composite short fiber is mainly composed of an ethylene-based polymer, and specifically, is a blended structure of an ethylene-based polymer and a propylene-based polymer, or a copolymer of propylene. It is composed of a polymerized ethylene copolymer.

[0010] For example, when the sheath is formed of a single component of low-density polyethylene, a problem arises because the nonwoven fabric has a slimy feeling. Further, when the sheath portion is composed of a single component of high-density polyethylene, the spinnability is reduced, and it becomes difficult to obtain fibers of fineness. On the other hand, by adopting a blend structure or a copolymer structure as in the present invention, even when low-density polyethylene is applied, it is possible to prevent the occurrence of slimy feeling due to the influence of polypropylene, and to apply high-density polyethylene. Even though, the spinnability can be improved, so that fibers of fine fineness can be obtained.

In general, an ethylene polymer has lower elongation characteristics than a propylene polymer at the same spinning speed. Therefore, when spinning and drawing a conjugated fiber having a core-in-sheath structure in which the propylene-based polymer is disposed in the core and the ethylene-based polymer is disposed in the sheath, the sheath is unlikely to follow the spinning-drawing stress in the core. Therefore, peeling of the core-sheath layer is apt to occur, and yarn breakage due to the separation is liable to occur, resulting in poor spinnability. Under such circumstances, when the sheath has a blend structure in the present invention, the propylene-based polymer is microscopically blend-dispersed in the ethylene-based polymer of the sheath, so that the spin-drawing stress is applied to the core. The elongation characteristics of the sheath portion when the occurrence is improved are improved, and as a result, the peeling of the core-sheath layer can be eliminated, and the spinnability can be improved. Therefore, it is possible to obtain a nonwoven fabric composed of fibers of fineness. it can.

Examples of the ethylene polymer include linear low-density polyethylene, low-density polyethylene, medium-density polyethylene, high-density polyethylene, and copolymerized ethylene mainly composed of ethylene.

Examples of the propylene-based polymer include polypropylene and copolymerized propylene mainly composed of propylene. The mixing ratio (weight ratio) of the ethylene polymer (hereinafter referred to as "a") and the propylene polymer (hereinafter referred to as "b") of the blend, that is, the blend ratio a / b is 99.5.
/0.5 to 75/25 is preferred. When the weight ratio of the propylene-based polymer is increased, the properties of the propylene-based polymer are increased and the spinnability is deteriorated.
On the other hand, when the propylene-based polymer is less than the above range, uniform mixing becomes difficult, not only it becomes difficult to obtain fineness yarn without improving the spinnability, but also peeling off from the core occurs, It is not good because the slimy feeling peculiar to polyethylene appears and the use is limited. Therefore, the mixing ratio is more preferably from 95/5 to 80/20.

When the sheath is a copolymer, so-called random copolymerization is preferred for copolymerization from the viewpoint of improving spinnability. In the case of this copolymer, the reason why the spinnability is improved is not clear, but it is considered that the propylene copolymerized improves the elongation characteristics of the polymer itself during spinning and stretching. Further, at the interface between the sheath and the core of the propylene-based polymer, the affinity between the sheath and the core is improved, whereby the peeling of the core-sheath layer can be eliminated.
As a result, the spinnability can be improved, and fibers with fineness can be obtained.

The ethylene copolymer may be copolymerized with at least 0.2% by weight of propylene. If the copolymerization amount of propylene is too large, the spinnability is reduced, the properties of polypropylene are too strong, and the melting point is significantly reduced, which is not preferable. On the other hand, if the copolymerization amount of propylene is too small, the properties of polyethylene become strong and a slimy feeling appears, or the interlayer between the sheath and the core is peeled off, which is not preferable. Therefore, the content is preferably set to 0.5 to 5% by weight.

On the other hand, in any case where the sheath portion is a blend structure or a copolymer, the propylene-based polymer constituting the core portion includes polypropylene or copolymerized propylene mainly composed of propylene. .

The conjugate ratio (weight ratio) of the core-sheath conjugate fiber must be sheath / core = 3/1 to 1/3. When the weight ratio of the sheath part is large, the heat bonding component increases and the fiber strength decreases, and when it is spread on a heat bonding nonwoven fabric, the texture becomes hard or lacks bulkiness, which is not preferable.
Further, when the weight ratio of the core portion is increased, the fiber strength is increased. However, when developed into a heat-bonded non-woven fabric, insufficient adhesion between fibers occurs, and a problem that the strength of the non-woven fabric is reduced is not preferable. The composite form may be a common concentric core-sheath structure, an eccentric core-sheath structure, or a modified cross-section.

The single fiber fineness of the fiber according to the present invention is 1 denier.
Must be less than or equal to This is because the smaller the single yarn fineness, the larger the number of fibers per constituent nonwoven fabric, and the higher the bulkiness and flexibility. The lower limit is about 0.2 denier from the current spinneret accuracy.

In the core-sheath type composite fiber, the sheath and the core preferably have a birefringence of 0.030 or more and a maximum heat shrinkage stress of the fiber of 0.015 g / denier or less. The birefringence of a fiber means the degree of crystal orientation of the fiber itself, and a larger value indicates a higher orientation. When the birefringence of both the sheath and the core is less than 0.030, the orientation of the fibers is reduced, so that the fiber strength and the fiber modulus are reduced, and a bulky and strong heat-bonded nonwoven fabric cannot be obtained. For this reason, the birefringence is more preferably 0.035 or more. The birefringence referred to here was measured using a Karl Zeiss Jena interference microscope, using a liquid mixture of liquid paraffin and α-bromonaphthalene as an encapsulant, and treating the polymer component in the sheath of the composite fiber with the core. The birefringence of each of the polymer components was measured.

Next, the maximum heat shrinkage stress of the fiber is an index of the shrinkage force during the heat treatment, and the larger the value, the higher the fiber shrinkage. In particular, fibers for heat-bonded nonwoven fabrics
If the shrink force is high at the time of thermal bonding, the formation, thickness and width of the obtained non-woven fabric will vary, which is a problem. Therefore, the smaller the maximum heat shrinkage stress, the more stable and high-quality nonwoven fabric can be obtained. From this, more preferably 0.0
The content is preferably 10 g / denier or less.

Next, a method for producing the core-sheath type composite fiber will be described. This fiber can be produced by melt composite spinning, and the melt composite spinning can be performed using a general composite spinning apparatus. At the time of melt composite spinning, a core-sheath type spinneret is used, and generally, composite spinning may be performed at a spinning temperature of 200 ° C to 280 ° C.

In the case where the sheath portion is a blend structure, the ethylene polymer (a) which is one component of the blend as the sheath component is, as described above, a linear low density polyethylene, a low density polyethylene, a medium density polyethylene,
Examples include high-density polyethylene, copolymerized ethylene mainly composed of ethylene, and the like. The melt index value of this ethylene polymer (a) is 10 to 50 g / 10
Need to be minutes. If it is less than 10 g / 10 minutes, the melt viscosity is too high, and the spinnability decreases. Also,
Means for lowering the apparent melt viscosity by raising the spinning temperature are not preferable because a large amount of smoke is generated and the working environment is deteriorated. Furthermore, when blended with a propylene-based polymer, there is a problem that microdispersion cannot be performed. On the other hand, when the melt index value exceeds 50 g / 10 minutes, the melt viscosity becomes too low, causing a decrease in fiber strength or a decrease in spinnability.

The propylene-based polymer (b), which is the other component as a blend of the above-mentioned sheath component, includes polypropylene or copolymerized propylene mainly composed of propylene as described above. The melt flow rate of this propylene polymer (b) is
It is necessary to be 5-45 g / 10 minutes. If it is not in this range, a uniform micro-blend structure with the ethylene-based polymer will not be obtained. That is, the melt flow rate value is 5
If it is less than g / 10 minutes, the dispersibility in the ethylene polymer will decrease. On the other hand, if it exceeds 45 g / 10 minutes, the dispersibility of the ethylene polymer in the propylene polymer decreases. This is because it is a combination of polymers incompatible with each other. Therefore, 5-45 g / 10
Minutes, more preferably 10 to 40 g / 10 minutes.

The mixing ratio (weight ratio) a / b of the ethylene polymer (a) and the propylene polymer (b) in the blend of the sheath component is 99.5, as in the case of the fiber itself.
/0.5 to 75/25 is preferred, and 95/5 to 80/2
0 is more preferred.

When the sheath is a copolymer, it is necessary to use an ethylene copolymer obtained by copolymerizing propylene as described above, as the ethylene copolymer serving as the sheath component. That is, it is necessary to copolymerize propylene in order to prevent the sliminess of polyethylene and improve spinnability. Since the spinnability can be improved, fibers with finer fineness can be obtained. In addition, the ethylene polymer of the sheath component and the propylene polymer of the core component are a combination of components that are not compatible with each other, but by copolymerizing propylene, an affinity is imparted, and Since the separation between the core and sheath layers can be eliminated,
The spinnability and physical properties of the conjugate fiber can be improved.

This ethylene copolymer may be copolymerized with at least 0.2% by weight of propylene, more preferably at 0.5 to 5% by weight, as in the case of the fiber itself. . In addition to this propylene, butene, pentene,
Hexene, octene, and the like may be copolymerized within a range not alienating the present invention.

The density of the ethylene copolymer of the sheath component is not particularly limited, but may be 0.92 to 0.96 g / cm.
³ is fine. It is necessary that the melt index value of the ethylene polymer of the sheath component is 10 to 50 g / 10 minutes. If it is less than 10 g / 10 minutes, the melt viscosity is too high, and the spinnability decreases. Also, means for raising the spinning temperature to lower the apparent melt viscosity is not preferable because a large amount of smoke is generated and the working environment is deteriorated. On the other hand, if the melt index value exceeds 50 g / 10 minutes, the melt viscosity is too low, which causes a problem because the fiber strength is reduced or the spinnability is reduced.

On the other hand, the propylene-based polymer may be used as the core component regardless of whether the sheath has a blend structure or a copolymer. That is, examples of the polymer to be applied include polypropylene and copolymerized propylene mainly composed of propylene. The propylene polymer has a melt flow rate of 5 to 45.
g / 10 minutes.

Outside this range, there arises a problem that the spinnability decreases due to the difference in the ballast effect between the sheath and the core of the fiber. That is, when the melt flow rate is less than 5 g / 10 minutes, the melt viscosity becomes extremely high, and the spinnability decreases. Even if the apparent melt viscosity is lowered by increasing the spinning temperature, the same can be said because the melt viscosity of the sheath greatly decreases.In addition, there is a problem that smoke generation increases and the environment of the spinning chamber deteriorates. Become. Also,
If it exceeds 45 g / 10 minutes, the modulus of the fiber is reduced, and only a fiber with no stiffness can be obtained. Further, when applied to a heat-bonded nonwoven fabric, there is a problem that the bulkiness is greatly reduced. Therefore, it is preferable to set it to 5 to 45 g / 10 minutes,
More preferably, it is 40 g / 10 minutes.

In the composite spinning, the Q value (weight average molecular weight / number average molecular weight) of the ethylene polymer component (a) of the sheath component after melting is preferably 8 or less. The Q value is the ratio of the weight average molecular weight to the number average molecular weight of the polymer determined by gel permeation chromatography, and is individually collected before melt-weighed polymers are subjected to composite spinning. This is a value measured using a cooled polymer as a sample. It is known that a thermoplastic polymer is liable to be deteriorated by the influence of heat and shear force applied during melt spinning, and that the Q value after melt spinning is lower than that before spinning. The Q value indicates the width of the molecular weight distribution, and has a great influence on the appropriateness of production and processing of the conjugate fiber. That is, if the Q value is large and the width of the molecular weight distribution is wide,
A stable conjugate fiber can be obtained, and when developed for heat-bonded non-woven fabric applications, the heat treatment temperature range becomes wider,
A nonwoven fabric of stable quality can be obtained. However, if the Q value increases and the width of the molecular weight distribution becomes too wide, the yarn cooling during melt spinning deteriorates, and the spinnability decreases. Therefore, the Q value is preferably 8 or less, and
0 or less is more preferable.

On the other hand, the Q value (weight average molecular weight / number average molecular weight) of the propylene polymer component of the sheath component and the core component after melting is preferably 2 or more and 8 or less. As described above, this Q value indicates the width of the molecular weight distribution, and has a great influence on the appropriateness of production and processing of the conjugate fiber. In particular, the propylene-based polymer component is a high melting point component of the conjugate fiber and represents the fiber modulus, and the width of the molecular weight distribution is particularly important. That is, when the Q value is less than 2, the molecular weight distribution is narrowed and the shrinkage of the conjugate fiber is reduced, which is a preferable direction, but the crimp holding property when crimping the conjugate fiber is reduced. The most commonly used car for web formation
In this case, it is difficult to successfully pass the metallization process. In addition, the heat treatment temperature range for heat-bonding the nonwoven web or nonwoven fabric after passing through the carding process by using a heat treatment device such as an emboss roller or a hot air drier is narrowed, and the bulkiness is increased. And a high-quality nonwoven fabric cannot be stably obtained. Furthermore, since the toughness of the conjugate fiber is reduced, a nonwoven fabric having excellent bulkiness and flexibility cannot be obtained. On the other hand, if the Q value exceeds 8, the width of the molecular weight distribution of the polymer becomes too wide, and the yarn cooling during melt spinning is deteriorated, the spinnability is reduced, and it is possible to obtain a conjugate fiber having fineness. It will be difficult. Therefore, this Q value is 2 or more and 8
Or less, preferably 3 or more and 7 or less.

The sheath / core composite ratio (weight ratio) at the time of producing the core-in-sheath composite fiber is the same as in the case of the core-in-sheath composite fiber itself.
3/1 to 1/3 are required. Further, at the time of melt composite spinning, the discharge linear velocity of the ethylene-based polymer component and the propylene-based polymer component in the sheath component was set to 1.7 to 5.8.
m / min / denier is preferred. The discharge linear velocity referred to here is a single hole discharge amount Q (g / min) of the molten polymer,
The melt density ρ (g / cm ³ ) of the polymer and the spinning hole diameter d (m
m) and the target single yarn fineness D (denier), which is calculated by the following equation (i). The melt density ρ was determined using a melt indexer manufactured by Toyo Seiki Co., Ltd., using the core component polymer or the sheath component polymer as a sample, setting the temperature conditions to the spinning temperature to be applied, and setting the core component for each of the two samples. The melt density of the polymer and the melt density of the sheath component polymer are determined by the following equation (ii), respectively, and the melt densities of the obtained samples are obtained by weighted averaging.

Discharge linear velocity (m / min / denier) = 4 Q / (πρd ² ) / D (i) Melt density (g / cm ³ ) = FR × t / s × L (Ii) FR: A polymer melted at the spinning temperature was used as a sample, and an applied load was used.
Flow rate value (g / 10
Min) s: average cross-sectional area of piston and cylinder x 600 (c
m ² ) L: moving distance of the piston (cm) t: time required for the piston to move the distance L (seconds) Usually, when melt-spinning a composite fiber composed of different kinds of polymers, the melt flow between the combined polymers is used. -The spinnability is greatly affected by the difference in spinning range due to the rate difference and the melting temperature defined by the high viscosity component, and it is necessary to select an appropriate discharge linear speed according to the type of polymer. Therefore, in order to obtain good spinnability, the discharge linear velocity should be 1.7 to
It is preferable to be 5.8 m / min / denier, and when obtaining fine fibers, if the ejection linear velocity is out of this range, the spinnability tends to decrease. That is, if it is less than 1.7 m / min / denier, yarn breakage tends to occur. In addition, 5.8m
If it exceeds / minute / denier, the spinnability deteriorates because stains are generated on the surface of the nozzle cap, and the spinning tension is lowered to make uniform cooling difficult. Therefore, the density is preferably 2.0 to 5.0 m / min / denier, and particularly preferably 2.5 to 4.0 m / min / denier.

In addition, a matting agent, a light-fast agent, a heat-resistant agent, a pigment, and the like, which are usually used for fibers, are added to both the sheath and core components as long as the effects of the present invention are not impaired. be able to.

Next, the undrawn conjugate fiber obtained by melt conjugate spinning is hot drawn at 50 ° C. or higher and at a temperature at which the fibers do not fuse with each other. The hot stretching can be performed using an ordinary hot stretching apparatus. Usually, when a thermoplastic synthetic fiber is stretched, it is known that heating and stretching is performed at a temperature equal to or higher than the glass transition temperature.
Thermal stretching is performed at the above temperature. When the stretching temperature is lower than 50 ° C., the stretching tension becomes too high, and the stretchability is reduced. The stretching temperature is at most lower than the temperature at which the fibers start to fuse with each other. If the drawing temperature is too high and the fibers start to fuse with each other, yarn breakage occurs in the drawing step, and the operability is lowered, or the uniformity of the product is lowered, so that the quality is lowered. . Therefore, the stretching temperature is set to 50 ° C. or higher and a temperature at which the fibers are not fused to each other, preferably 60 to 100 ° C.

Next, when applying a crimping treatment to the obtained stretched conjugate fiber, a crimping device such as a stuffer-type crimping device is usually used. Subsequent to the crimping treatment, a finishing oil is applied to the fiber, dried, and then cut into a predetermined length to obtain a short fiber. The fiber length in this case is usually 32 to
A range of 76 mm applies.

In order to produce this fiber, the single fiber fineness of the conjugate short fiber must be 1 denier or less.
If the single fiber fineness exceeds 1 denier, the flexibility of the non-woven fabric is reduced, or the cooling of the ethylene-based or propylene-based molten polymer becomes insufficient during melt spinning, and fusion between the filaments occurs. It is not preferable because the spinning property occurs and the spinnability is reduced.

The heat-bonded nonwoven fabric of the present invention needs to be composed of an aggregate in which the conjugate fibers are oriented. This is because when the conjugate fiber is stretched and oriented, embrittlement of the conjugate fiber due to heat treatment in the nonwoven fabric manufacturing process is reduced, leading to quality stability of the nonwoven fabric.

Further, the nonwoven fabric according to the present invention needs to be bonded at the bonding point between the fibers. This is necessary from the viewpoint of maintaining the shape of the nonwoven fabric, and the web is composed of the composite fibers so that the fibers are bonded at the bonding points between the fibers. That is, the sheath component of the core-sheath composite fiber is melt-bonded at the contact point between the fibers. Moreover, since the sheath component has an affinity for the core portion, there is no peeling between the core and sheath components, and since it is composed of ultrafine fibers, the number of constituent fibers increases, and the melt-bonded portion at the fiber contact point increases. As a result, the form of the nonwoven fabric is firmly held, the strength is high, and the nonwoven fabric is bulky and characteristic.

Next, the physical properties of the heat-bonded nonwoven fabric according to the present invention will be described. First, the strength of the nonwoven fabric will be described.
Since the nonwoven fabric of the present invention is composed of the ultrafine conjugate fibers, the contact points between the fibers are bonded in a state where the number of constituent fibers per unit weight is larger than that of the conventional fineness. Moreover, since there is no separation between the core and the sheath, the binder component of the sheath sufficiently acts on the adhesion between the fibers, and the strength of the nonwoven fabric is increased. Therefore, in the present invention, the strength is preferably 5 kg / 2.5 cm or more, more preferably 6 kg / 2.5 cm or more.
This is regulated because of its practicality.
If the width is less than 2.5 cm, general-purpose applications are hindered.

The bulkiness is the bulkiness of the nonwoven fabric. The smaller the value, the higher the bulkiness. In the nonwoven fabric according to the present invention, the bulk density is 0.03.
０．０0.06 g / cm ³ is preferred. Bulk density is 0.06 g /
If it exceeds cm ³ , the nonwoven fabric cannot be said to be bulky, and the goodness of the fine fibers cannot be utilized. The smaller the bulk density is, the higher the bulk density is. However, as the fiber becomes ultrafine, the Young modulus of the single fiber itself decreases, and the bulk density tends to increase. Therefore, 0.03 g / cm
It is difficult to manufacture a nonwoven fabric of less than ³ from the current state.

The air permeability is a degree at which gas passes, and a smaller value indicates a smaller degree. The air permeability of the nonwoven fabric according to the present invention is 45 cc / cm ² · s
The following is preferred. If the air permeability exceeds 45 cc / cm ² · s, the degree of passage of the gas becomes high, so that there are restrictions in application such as a decrease in heat retention effect and a decrease in dust removal performance, which is not preferable.

Next, regarding the coefficient of friction (MIU) of the nonwoven fabric, the MIU of the nonwoven fabric according to the present invention is preferably 0.18 or more. When the MIU is less than 0.18, the nonwoven fabric is liable to slip, resulting in various problems. For example, when applied as a coaster or simple rug,
The nonwoven fabric or the like is moved by just touching, and problems such as breakage of objects are likely to occur.

Finally, regarding the water retention, this is the performance of retaining moisture, and the higher the value, the better the retention of moisture. In the nonwoven fabric according to the present invention, the water retention is preferably 200% or more. If the water retention is less than 200%, it cannot be said that the water retention is good. For example, when applied to a dry battery separator, the retention performance of the electrolytic solution is reduced, causing a problem.

The basis weight of the non-woven fabric according to the present invention is not particularly limited, but when used as a medical hygiene material, it is 150 g / m 2.
² or less, 10 when used as dry cell separator
0 g / m ² or less is usually applied.

Next, a method for producing a nonwoven fabric according to the present invention will be described. First, the short fibers are prepared, and the short fibers are opened, weighed, and passed through a card machine to prepare a card web. The card machine is preferably a flat card machine for fine denier. This is because a general card machine with a rough needle gauge generates a lot of neps and deteriorates the quality of the web. The fibrous web is then bonded at the points of contact between the fibers to form a nonwoven. As a method of bonding the fiber webs at the contact points between the fibers, for example, the sheath component of the constituent fibers is melt-bonded by hot air such as a heat circulating heat treatment machine or a hot air dryer and the suppression thereof, thereby contacting the fibers. A method of bonding at a point can be used. As the heat treatment conditions, a minimum suppression of hot air is necessary to melt-bond the sheath components of the fibers constituting the web. However, in the present invention, the following conditions are indispensable in the case of a heat circulation type heat treatment machine. is there.

Heat treatment temperature T (° C.) Tm1 ≦ T ≦ Tm2-10 Heat treatment time t (min) 0.1 ≦ L / v, L / v
= T Tm1: Melting point of the ethylene polymer in the sheath (° C.) Tm2: Melting point of the propylene polymer in the core (° C.) L: Length of the heat treatment zone (m) When the melting point is lower than the melting point of the polymer, the ethylene polymer does not melt and the fibers do not adhere to each other, so that the shape of the nonwoven fabric cannot be maintained.
Further, when the heat treatment temperature T exceeds a temperature lower by 10 ° C. than the melting point of the propylene polymer in the core, the propylene polymer in the core softens and the heat shrinkage of the constituent fibers itself increases, The nonwoven fabric has a hard texture, and the effect of the present invention using the ultrafine fibers cannot be seen. Therefore, a more preferable heat treatment temperature T (° C.) is Tm1-5 ≦ T ≦ T
m2-14, and most preferably Tm1-10 ≦ T
≤ Tm2-18.

If the heat treatment time t is less than 0.1 minute, the sheath component of the fibrous web is not uniformly melted and adhesion unevenness is generated, so that a uniform nonwoven fabric with high nonwoven fabric strength cannot be obtained.

[0049]

The present invention will be described in more detail with reference to the following examples. In addition, the measuring method of the physical property value shown in the following Examples is as follows. (1) Melt index value (hereinafter simply abbreviated as MI value) It was measured by the method described in ASTM D1238 (E). (2) Tensile strength and elongation of fiber Tensilon UTM-4-1-10 manufactured by Toyo Boldwin Co., Ltd.
Using 0, a sample having a sample length of 20 mm was measured at a tensile speed of 20 mm / min. (3) Tensile strength of nonwoven fabric According to the slip method described in JIS L-1096, ten test pieces having a width of 2.5 cm and a sample length of 10 cm are prepared.
The maximum tenacity was individually measured under the condition of a tensile speed of 10 cm / min, and the average value was taken as the tensile tenacity. (4) Tensile elongation of nonwoven fabric The elongation at the maximum tensile strength measured by the above method was defined as the tensile elongation. (5) Bulk density of nonwoven fabric A total of five specimens each having a sample width of 10 cm and a sample length of 10 cm were prepared, and the basis weight (g / m ² ) was measured for each specimen, and then the thickness was measured by Daiei Kagaku Seiki Seisaku-sho, Ltd. 4.5 g /
applying a load of cm ^2, thickness after leaving for 10 seconds (m
m) was measured, the bulk density was calculated by the following equation, and the average value was taken as the bulk density of the nonwoven fabric.

Bulk density (g / cm ³ ) = (basis weight) / (thickness) / 1000 (6) Air permeability of non-woven fabric A test piece is obtained by a method described in JIS-1096 using a fragile type testing machine. The amount of air (cc / cm ² / sec) passing through was determined, and the result was indicated by an average value of five test pieces. (7) Non-woven fabric MIU Using a friction tester, KES-SE (manufactured by KATO-TECH), a weight of 0.5 mm-diameter piano wire bent into a U-shape is placed on a contact with ten contacts. To give a force of 50 g, and the contact surface was pressed against the sample nonwoven fabric. This sample nonwoven fabric is horizontally moved by 2 cm at a constant speed of 0.1 cm / sec.
It was moved, and five friction coefficients in the moving area were measured in each of the vertical direction and the horizontal direction, and the average value was obtained to obtain the MIU. (8) Water retention of nonwoven fabric Prepare three sample pieces of 25 cm x 25 cm in advance,
After measuring the weight (W0) of this sample piece, place it in distilled water.
Soaked for hours. Thereafter, the sample pieces were taken out, squeezed lightly one by one with a glass rod, and the weight (W1) was measured again. Then, the water retention was calculated according to the following formula, and the water retention was indicated by the average value of three sample pieces.

Water retention rate (%) = 100 (W 1 −W 0) / W 0 (Example) As the core-sheath type composite short fiber A, the following A-1 was used in advance.
~ A-8 fibers were prepared.

A-1 An ethylene copolymer having a density of 0.951 g / cm ³ , a melting point of 129 ° C., a Q value of 4, a melt index value of 25 g / 10 min, and 1.5% by weight of propylene random copolymer was prepared. As a sheath component, density 0.920 g / cm ³ , melting point 16
2 ° C, Q value 6.5, melt flow rate value 30g / 10
The propylene-based polymer as the core component was melted by a usual extruder-type extruder. Thereafter, using a core-sheath type composite spinneret having a spinning hole diameter of 0.5 mm and a number of holes of 390, the single hole discharge amount was 0.11 g / min, that is, the ratio (weight ratio) of the core component and the sheath component was 1/1. The spinning was performed at a spinning temperature of 230 ° C. and the yarn was drawn at a drawing speed of 1100 m / min to obtain an undrawn yarn of a core-sheath type composite filament yarn.
Dozens of the obtained undrawn yarns were converged and heat drawn as a tow. At the time of stretching, a two-stage heat roller stretching machine was used, and the stretching conditions were a stretching speed of 100 m / min and a first roller.
The film was stretched at a temperature of 65 ° C., a second roller temperature of 90 ° C., and a third roller temperature of 25 ° C. at a stretching ratio of 90% of the maximum stretching ratio. Continuing with the drawing, the drawn tow is supplied to a stuffer box to give a crimp of 14 pieces / 25 mm, and then a finishing oil is applied and dried at a temperature of 70 ° C. to obtain a single fiber fineness of 0.6 denier. Thus, raw cotton of a core-sheath type composite short fiber having a fiber length of 38 mm was obtained. The obtained raw cotton has a high elongation of 3.8 g.
/ Denier, 88%.

A-2 The spinning and drawing was carried out under the same conditions as in A-1 except that the discharge rate of each single hole was 0.08 g / min, and the single fiber fineness was 0.4 denier.
The raw cotton of the core-sheath type composite short fiber having a fiber length of 32 mm was obtained.
The strong elongation of the obtained raw cotton was 3.6 g / denier, 89%.

A-3 Spinning and drawing were carried out under the same conditions as in A-1 except that the discharge rate of each single hole was 0.23 g / min, and the fineness of the single fiber was 1.0 denier.
The raw cotton of the core-sheath type composite short fiber having a fiber length of 38 mm was obtained.
The strong elongation of the obtained raw cotton was 4.5 g / denier, 88%.

A-4 linear low-density polyethylene having a density of 0.936 g / cm ³ , a melting point of 125 ° C., a Q value of 3, and a melt index value of 43;
5. density 0.919 g / cm ³ , melting point 163 ° C, Q value
And a propylene polymer blended at a weight ratio of 90/10 with a melt flow rate of 15 g / min as a sheath component, having a density of 0.920 g / cm ³ , a melting point of 163 ° C., and Q
A propylene polymer having a value of 6.0 and a melt flow rate of 30 g / min was used as a core component. These were melted by a usual extruder-type extruder, and then the spinning hole diameter was adjusted to 0.
Spinning at 230 ° C. using a core-sheath type composite spinneret having a diameter of 5 mm and a number of holes of 300, the discharge amount of each single hole being 0.11 g / min, that is, the composite ratio (polymerization ratio) of the core component and the sheath component being 1/1. It was melt-spun at a temperature and was drawn at a drawing speed of 1100 m / min to obtain an undrawn yarn of a core-sheath type composite filament yarn. Dozens of the obtained undrawn yarns are converged into a tow, hot-drawn by the same method as that of the A-1 raw cotton, dried at a temperature of 70 ° C., and a single fiber fineness of 0.6 denier. Thus, raw cotton of a core-sheath type composite short fiber having a fiber length of 38 mm was obtained. The obtained raw cotton had a high elongation of 3.7 g / denier and 90%.

A-5 A high-density polyethylene having a density of 0.961 g / cm ³ , a melting point of 136 ° C., a Q value of 4, and a melt index value of 20 was used as a sheath component, a density of 0.920 g / cm ³ , a melting point of 163 ° C., and a Q value of 6 A propylene polymer having a melt flow rate of 30 g / min. These were melted with a normal extruder-type extruder, and then the spinning hole diameter was 0.5 mm.
Spinning at 230 ° C. using a core-sheath type composite spinneret having a diameter of 390 mm and a hole number of 390, and a single hole discharge amount of 0.5 g / min, ie, a composite ratio (polymerization ratio) of the core component and the sheath component of 1/1. It was melt-spun at a temperature and was drawn at a drawing speed of 1100 m / min to obtain an undrawn yarn of a core-sheath type composite filament yarn. Dozens of the obtained undrawn yarns were converged into a tow, hot-drawn by the same method as that of the A-1 raw cotton, and dried at a temperature of 70 ° C.
Raw cotton of a core-sheath type composite short fiber having a single fiber fineness of 2 denier and a fiber length of 51 mm was obtained. The strength and elongation of the obtained raw cotton is 4.7 g /
Denier, 91%.

A-6 An ethylene polymer having a density of 0.936 g / cm ³ , a melting point of 126 ° C., a Q value of 4, and a melt index value of 43 g / 10 minutes, a density of 0.920 g / cm ³ , a melting point of 162 ° C.
A component obtained by blending a propylene polymer having a value of 6.5 and a melt flow rate of 15 g / 10 minutes with a weight ratio of 90/10 was used as a sheath component. In addition, the density is 0.920
g / cm ³ , melting point 162 ° C., Q value 6.5, melt flow
A propylene polymer having a late value of 30 g / 10 minutes was used as a core component. These were melted by a usual extruder-type extruder, and then a core-sheath composite undrawn yarn was collected under the same spinning conditions as for the A-1 raw cotton. Subsequently, stretching was performed according to A-1 raw cotton, and the single fiber fineness was 0.6 denier and the fiber length was 38 m.
m of core-sheath type composite short fiber was obtained. The obtained raw cotton had a high elongation of 3.9 g / denier and 89%.

A-7 An ethylene polymer having a density of 0.936 g / cm ³ , a melting point of 126 ° C., a Q value of 4, and a melt index value of 43 g / 10 minutes, a density of 0.920 g / cm ³ , a melting point of 162 ° C.
Conditions for producing A-6 raw cotton, except that a component obtained by blending a propylene-based polymer having a melt flow rate of 15 g / 10 minutes with a propylene-based polymer at a weight ratio of 98/2 was used as a sheath component. Using a single fiber fineness of 0.6 denier and a fiber length of 3
A raw cotton of a core-sheath type composite short fiber of 8 mm was obtained. The obtained raw cotton had a high elongation of 3.8 g / denier d and 88%.

A-8 An ethylene polymer having a density of 0.951 g / cm ³ , a melting point of 135 ° C., a Q value of 4, a melt index value of 25 g / 10 min, and a random copolymerization of 0.2% by weight of propylene is sheathed. Except for using the components, the conditions under which A-3 raw cotton was produced were applied to obtain a raw fiber of a core-sheath composite short fiber having a single fiber fineness of 1.0 denier and a fiber length of 38 mm. The obtained raw cotton had a high elongation of 3.5 g / 92% denier.

Examples 1 to 4 and Comparative Example 1 A-1 to A-5 were used as the core-sheath composite short fibers, and these were supplied to a card machine (type 60-32) manufactured by Ikegami Kikai and opened. Thus, a basis weight of 50 g / m ² card web was prepared. This card web was subjected to a heat treatment at a heat treatment temperature of 140 ° C. by hot air using a continuous heat treatment machine (heat treatment zone 160 cm) manufactured by Tsujii Senki Kogyo.
The heat treatment was performed at a temperature of 100 ° C., a hot air flow of 100 m ³ / min, and a heat treatment time of 25 seconds. Table 1 shows the physical properties of the obtained nonwoven fabric.

[0061]

According to the present invention, the sheath is made of a specific ethylene polymer, that is, a blend structure of an ethylene polymer and a propylene polymer or an ethylene polymer obtained by copolymerizing propylene. In these blended structures and copolymers, the elongation properties of the sheath during spinning and stretching are improved, while in the case of the copolymer, the sheath is further provided with an affinity for the core propylene-based polymer. In addition, the peeling of the core-sheath layer is eliminated, and thus the spinnability is improved, and a nonwoven fabric made of fine fibers can be obtained. That is, the heat-bonded nonwoven fabric of the present invention is composed of a polyolefin-based ultrafine core-sheath composite short fiber, and therefore has high nonwoven fabric strength, extremely excellent flexibility, and is very bulky and extremely excellent in water retention. In addition, since the fiber used as the sheath structure is composed of a blend structure of an ethylene-based polymer and a propylene-based polymer or an ethylene-based polymer in which propylene is copolymerized, it does not have a slimy feeling peculiar to polyethylene. It has good texture and good texture. Therefore, it is particularly suitable for use in medical hygiene materials such as disposable diapers and sanitary napkins. In addition, since it has chemical resistance and excellent water retention, it is particularly suitable as a battery separator. In addition, it can be applied to a wide range of uses such as agricultural and horticultural materials, packaging materials and filters as living-related materials.

As is apparent from Table 1, in Examples 1 to 4, the smaller the single fiber fineness, the higher the strength,
It can be seen that a nonwoven fabric having excellent water retention can be obtained. In Comparative Example 1, since the single fiber fineness was large, the number of fibers constituting the nonwoven fabric was reduced, so that the nonwoven fabric had high air permeability and poor water retention.

Examples 5 and 6, Comparative Examples 2 to 4 The same conditions as in Example 1 except that a card web was prepared in the same manner as in Example 1 and the heat treatment temperature and the heat treatment time were changed as shown in Table 2. A non-woven fabric was prepared. Table 2 shows the obtained results.

[0064]

[Table 2]

As is evident from Table 2, the nonwoven fabric of Example 5 has high strength and is excellent in water retention. In Example 6, although the heat treatment time is long, there is a problem from the viewpoint of productivity, but it can be seen that the obtained nonwoven fabric has high strength and excellent water retention.

In Comparative Example 2, since the heat treatment temperature was too high, the core component constituting the fibers was also softened, the web was severely shrunk, the texture was very hard, and it could not be said that it was a nonwoven fabric. In Comparative Example 3, since the heat treatment temperature was too low, the whole did not fuse at the contact points of the fibers, and a high strength nonwoven fabric could not be obtained. In Comparative Example 4, although the heat treatment time was short and the front surface of the web was fused at the contact point of the fibers, the back surface was not fused and only a fluffy product was obtained. Example 7 A web was prepared using the raw fiber A-6 of the core-sheath type composite short fiber under exactly the same conditions as in Example 1, and then a nonwoven fabric was prepared. The nonwoven fabric performance is shown below. It can be seen that the nonwoven fabric of Example 7 has a clearly high strength and is excellent in water retention. Also, the texture of the nonwoven fabric was very excellent, and the texture was good.

Weight 50 g / m ² Tensile strength 11.4 kg / 2.5 cm Tensile elongation 39% Bulk density 0.042 g / cm ³ MIU 0.20 Air permeability 20 cc / cm ² s Water retention 760% Example 8 Core-sheath type A web was made using the composite short fiber raw cotton A-7 under the same conditions as in Example 1, and then a nonwoven fabric was made. The nonwoven fabric performance is shown below. It can be seen that the non-woven fabric of Example 8 is clearly strong and has excellent water retention. Also, the texture of the nonwoven fabric was very excellent, and the texture was good.

Weight 49 g / m ² Tensile strength 11.6 kg / 2.5 cm Tensile elongation 38% Bulk density 0.045 g / cm ³ MIU 0.35 Air permeability 21 cc / cm ² · s Water retention 765% Example 9 Core-sheath type A web was prepared using the composite short fiber raw cotton A-8 under exactly the same conditions as in Example 1, and then a nonwoven fabric was prepared. The nonwoven fabric performance is shown below. It can be seen that the non-woven fabric of Example 9 is clearly strong and has excellent water retention. Also, the texture of the nonwoven fabric was very excellent, and the texture was good.

Weight 49 g / m ² Tensile strength 9.2 kg / 2.5 cm Tensile elongation 37% Bulk density 0.032 g / cm ³ MIU 0.20 Air permeability 25 cc / cm ² · s Water retention 545%

[0070]

The heat-bonded nonwoven fabric according to the present invention is composed of polyolefin-based fine core-sheath conjugate short fibers, and therefore has a high strength of the nonwoven fabric, is bulky and has excellent water retention. In addition, since fibers having a specific ethylene-based polymer as a sheath component are used, it does not have a slimy feeling peculiar to polyethylene, has a very good texture, and has a good texture. Therefore, it is particularly suitable for use in medical hygiene materials such as disposable diapers and sanitary napkins. In addition, since it has chemical resistance and excellent water retention, it is particularly suitable as a battery separator. In addition, it can be applied to a wide range of uses such as agricultural and horticultural materials, packaging materials and filters as living-related materials.

──────────────────────────────────────────────────続 き Continued from the front page (72) Nobuo Noguchi 23, Uji Kozakura, Uji-city, Kyoto Unitika, Central Research Laboratory, Unitika Co., Ltd. (56) References Table 5-505856 (JP, A) (58) Fields surveyed (Int.Cl. ⁶ , DB name) D04H 1/54 D01D 5/34 D01F 8/06

Claims (7)

(57) [Claims] The present invention has a sheath formed of a blend structure of an ethylene-based polymer and a propylene-based polymer, and a core of a propylene-based polymer. A heat-bonded non-woven fabric comprising denier core-sheath composite short fibers and bonded at contact points between the fibers. 2. The mixing ratio of the ethylene-based polymer and the propylene-based polymer in the sheath portion is from 99.5 / 0.5 to 75/25 by weight as ethylene-based polymer / propylene-based polymer. The heat-bonded nonwoven fabric according to claim 1, wherein: 3. A monofilament having a sheath fineness of 0.2 to 1 denier, comprising a sheath formed of an ethylene polymer obtained by copolymerizing propylene, and a core of the propylene polymer. A heat-bonded nonwoven fabric comprising core-sheath composite short fibers and bonded at contact points between the fibers. 4. The copolymerization ratio of propylene in the copolymer of the sheath portion is 0.2% by weight or more and 5% by weight or less, and the copolymerization ratio of the ethylene polymer is 99.8% by weight or less and 95% by weight. The heat-bonded nonwoven fabric according to claim 3, wherein the content is not less than% by weight. 5. A strength of at least 5 kg / 2.5 cm width, a bulk density of 0.03 to 0.06 g / cm ³ , and an air permeability of 45 cc.
/ Cm ² · s or less, the coefficient of friction (MIU) is 0.18 or more, any one of claims thermal bonding nonwoven of claims 1 to water retention, characterized in that less than 200% up to 4. 6. A yarn having a sheath portion formed of a blend structure of an ethylene polymer and a propylene polymer, and a core portion of a propylene polymer, and having a single yarn fineness of 0.2 to 1 A method for producing a heat-bonded nonwoven fabric, comprising heat-treating a card web composed of denier core-sheath composite short fibers with hot air so as to satisfy the following formula, and bonding the fibers at contact points between the fibers. . Heat treatment temperature T (° C.) Tm1 ≦ T <Tm2−10 Heat treatment time t (min) 0.1 ≦ L / v, L / v = t Tm1: Melting point (° C) of ethylene polymer in sheath Tm2: Core L: Heat treatment zone length (m) v: Heat treatment rate (m / min) 7. A fiber having a sheath formed of an ethylene polymer obtained by copolymerizing propylene and a core of a propylene polymer and having a single fiber fineness of 0.2 to 1 denier. A method for producing a heat-bonded nonwoven fabric, comprising heat-treating a card web composed of a core-sheath composite short fiber with hot air so as to satisfy the following formula and bonding the card web at a contact point between the fibers. Heat treatment temperature T (° C.) Tm1 ≦ T <Tm2−10 Heat treatment time t (min) 0.1 ≦ L / v, L / v = t Tm1: Melting point (° C) of ethylene polymer in sheath Tm2: Core L: Heat treatment zone length (m) v: Heat treatment rate (m / min)